There has long been a strong interest in containing electric power consumption in electronic circuits which may depend upon limited power sources such as batteries or solar panels. Interest has been particularly acute for radiotelephone system stations that are either portable or located in a geographical area not adequately served by electric power distribution facilities. Such a station is herein usually called a subscriber station unit, or simply a subscriber unit. This interest has become even more sharply focused as concerns have grown about the need to contain pollution of various kinds.
In the radiotelephone field several types of efforts have been made to limit power consumption. Voice operated transmitters (VOX) are well-known wherein the presence or absence of an actual voice signal turns a transmitter power supply ON or OFF, and one example is the D. R. Bolgiano et al. U.S. Pat. No. 4,130,731. Otherwise a subscriber unit including such a transmitter is fully powered during all states of operation. A number of power conservation efforts have resorted to periodically enabling at least the receiving circuits of a subscriber unit while the unit is in a standby mode awaiting the availability of a channel or awaiting initiation of a call, and some examples are the U.S. Pat. Nos. 4,272,650 to D. R. Bolgiano et al., and 5,203,020 to H. Sato et al. Subscriber unit circuits in these latter systems are otherwise fully powered during actual call signal processing. The term "call signal processing" refers to operations such as, e.g., amplification, filtering, encoding/decoding, interpolating, or modulating with respect to signals of any type for communication between stations.
In the Sato et al. patent, when a subscriber unit in a mobile telecommunication system is in a location where it is unable to be served on any channels of the system, it is powered up periodically to check for the availability of an appropriate channel; and otherwise all components except a timer are powered down. When an available channel has been found, and while awaiting the start of a call, the central processing unit (CPU) and a timer are continuously powered up while the remainder of the unit is periodically powered up to check for the start of a call. Finally, during a call connection, the entire subscriber unit is continuously powered up.
In another group of systems, subscriber units are powered up or down as a group and special arrangements are provided to power up a subscriber unit if necessary when others are powered down. Some examples include U.S. Pat. Nos. 4,964,121 to M. A. Moore, 4,509,199 to M. Ichihara, and 4,577,315 to S. Otsuka. Similarly, in U.S. Pat. No. 4,713,809 to Y. Mizota, a relay station for a time division multiple access (TDMA) system is powered up in only those TDMA time slots in which a subscriber unit served by it is active.
Subscriber units for radiotelephone systems, such as the subscriber unit of the U.S. Pat. No. 5,008,900 to D. N. Critchlow et al., have included means for powering down a certain relatively high power consumption component at a selected time determined by the subscriber unit function being performed at such time. For example, in that Critchlow et al. patent a processor chip, included in the unit for controlling the various unit components as well as performing certain signal processing functions, is temporarily powered down when there is no phone call in progress. The powering down occurs in response to execution of an idle instruction in the unit's program of operation. Normal operation is temporarily resumed in response to an interrupt signal, and if there is no service routine to be performed the processor returns to the powered down state. Otherwise the subscriber unit components appear to be fully powered.
In the U.S. Pat. No. 4,675,863 to E. Paneth et al. a modem is operated in a half-duplex mode in a subscriber unit that functions in a TDMA environment. In that mode, the receiving demodulation section and the transmitting modulation section of the modem operate at different times; so the radio frequency (RF) section power amplifier is active for no more than half of the time. Other subscriber unit components appear to operate continuously.
Subscriber units in relatively difficult to reach locations often are equipped with a backup power supply using batteries supported by solar panels or an alternating current charger. In spite of efforts of the type described above, some subscriber units in wireless TDMA communication systems, which have the capability of being operated by backup battery power with appropriate charging facility, have had to use multiple backup batteries to supply the needed power. In some such units a pair of 15 ampere-hour 12-volt batteries and a charging source of four to six solar panels have been employed.